Orthopedic prosthetic knees are available from many manufacturers, including Intermedics Orthopedics, Inc., the assignee of our present invention. Such prosthetic knees typically comprise a tibial component and a femoral component. The tibial component replaces the condyle compartments on the proximal end of a patient's tibia. The femoral component replaces the distal end of the patient's femur and provides artificial condyles which articulate with the condyle compartments of the prosthetic tibial component. In addition, it is frequently necessary to provide an additional artificial surface on the patella. The patella rides between the condyles of the knee and provides an attachment point for various tenons. Because of the numerous tenons attached to the knee and its importance in controlling the mechanics of the knee, it is usually inadvisable to remove the patella entirely. However, it may be necessary to provide a new articulating surface adjacent the artificial condyles of the knee prosthesis. A prosthetic patella surface has been described, for example, in U.S. Pat. No. 4,888,021.
To attach such a prosthetic patella surface to the patella, a portion of the patella must be cut away and a surface prepared to receive the prosthesis. Various surgical apparatus and devices have been proposed to accurately and replicably assist in this operation. For example, a patella planer is described by Smith & Nephew Richards, Inc. in connection with their Genesis (tm) Total Knee System. Another type of planer has been described and sold by Biomet, Inc. in connection with their AGC (tm) Total Knee System. Similarly, an apparatus has also been provided by Dow Corning Wright Company for use with the Whiteside Ortholoc (tm) Modular Knee System. Johnson & Johnson has sold a device for preparing the patella in connection with the PFC (tm) Knee System.
In general, however, although a planer is employed with each of these systems, the planer has generally been used to finish the surface of the patella. A preliminary resection with a sagittal saw has been necessary to prepare the patella before planing. In many cases this has been necessary because of the variation in physiologic thickness of a patella from patient to patient.
With a foregoing in mind, we have invented a patella planer which can be used in a single operation to produce a resected surface on a patella, suitable for receiving an artificial prosthetic patella.
It has been a further object of our invention to provide a patella planer which could accommodate patellas of varying thickness.
Another important object of our invention has been to provide a patella planer which would stop cutting at a desired depth of cut, irrespective of the initial thickness of the patella.
These and other features are advantages of our invention will be apparent from the following description taken with reference to the accompanying drawings.